Middleweight champion Sergio Martinez checked in at 159 pounds for his fight against Julio Cesar Chavez last September.

And therein lies one of the stumbling blocks for a potential megafight.

"Sergio Martinez is 160. Floyd Mayweather walks around at 147," Mayweather said Sunday during a media appearance at the Final Four. "Where was Sergio Martinez when I was dominating when I was 21? Nowhere to be found."

Mayweather is busy preparing for a May 4 fight against Robert Guererro in the Las Vegas, the first in a potential six-fight deal with Showtime over the next 30 months.